Yui is a character from the Sword Art Online anime, novels and video games.
An AI in SAO created to take care of the mental health of the players but was suspended by the Cardinal system when the death game began. Unfortunately her monitoring operations continued and sensed the negative emotions such as fear, despair, rage, and madness from the players. Unable to perform her duty due to her restriction, she broke down due to errors. When she sensed Asuna and Kirito's more positive emotions, she was overcome with the urge to see them, which then kicked off the events of Morning Dew Girl and later made her their adoptive daughter.
In the XP4 fics, Yui is currently a member of the Heroes Coalition and serves as the Coalition's main A.I. She also attends Vanguard Academy as a student.
Yui had long, dark hair and bright black eyes. Her default equipment consisted of a one-piece white dress with a ribbon tied around her waist. She temporarily wore a long-sleeved pink sweater and a purple skirt, as well as red shoes (brown boots in the anime), during her time with Kirito and Asuna.
As a Navigation Pixie, Yui is ten centimeters-tall and wears a long, light-pink tube top dress with detached sleeves, pink anklets, and a blue flower in her hair.
As Yui was originally a girl without memories, she felt insecure about not knowing who or where her "parents" were. This led her to assume that Kirito and Asuna were her parents. After the couple decided to play along as the girl's parents due to the girl's psychological condition, she became cheerful and shows great affection for her so-called "parents". According to Asuna, her behavior was like that of a baby despite her child-like appearance. However, she lacked any sense of fear, regardless of the intensity of the danger she might be in and even showed signs of rebellion and recklessness when Kirito told her that she had to stay with Sasha when he and Asuna wanted to go to a dungeon to rescue Thinker.
After Yui regained her memories, she told her in-game parents that she had become melancholic when the death game began, as she was not allowed to comfort players and was forced to continue monitoring their psychological parameters. After nearly two years of only seeing insanity, misery, and anger, she finally noticed a couple, Kirito and Asuna, who showed happiness and joy and, even though she was not allowed to interact with players, she continued monitoring them and even came to the forest near their home to be close to the two to experience their emotions. After being comforted by Kirito and Asuna, she regained her joy. Even though she was about to be deleted by the Cardinal System, Yui showed no sign of repentance, but tears of happiness, for she was able to be with her in-game parents.
Upon being reactivated in ALfheim Online (ALO), Yui still displayed a deep attachment to Kirito and Asuna, continuing to act as a surrogate daughter. She also scolded Kirito when he received affection from other women aside from Asuna, stating her "papa" was "cheating", but she did, however, accept Leafa and later Sinon into Kirito's life.
Yui is a Blessed with an unnamed Gift. Her Gift gives her the ability travel around the entire multiverse through invisible lines, can jump from one device to another, control machines, hack computers, gather intel, and connect herself to many machines. She can connect to any ship's system no matter how far they are, even by light years.
- In the XP4 fics, Yui is the first A.I. Blessed in existence.
- Yui thinks that Kirito's most annoying habit is him napping anywhere and everywhere, as she gets sleepy from them too.
- Yui is able to hear other player's alarms.
- Yui's interest is breaking through firewalls.